1. Field of the Invention
The invention relates to a displacement compressor used as a supercharger for an automobile, a blower for an industrial machine, and so on.
2. Description of the Related Art
A displacement compressor is shown, for example, in the publication "TOKIKO REVIEW," Vol. 21, No. 4. This displacement compressor has a pair of rotors, each formed with two blades and having a zero degree twist angle. A recess 30 has a rectangle shape (shown in FIG. 8) and is formed in a chamber so as to be around an outlet 23 for the purpose of reducing the compressor noise. The recess 30 causes the operating chamber to open to the outlet 23 earlier and more gradually than in a compressor having no such recess. A rapid fluid flow from the operating chamber into the outlet 23 is thereby avoided or reduced. Therefore, pressure pulsations are reduced and the compressor noise is diminished.
FIG. 7 shows a device developed by the present inventors, which is not prior art with respect to the present application. It includes a displacement compressor 50 having a pair of three-blade helical rotors 51, 52 in a chamber 55, in which the fluid is exhausted continuously to the outlet 54 past the recess 53. Therefore, pressure pulsations are reduced and the compressor noise is diminished. Reference numerals 51a and 51b (52a and 52b) indicate seal faces of the rotors 51, (52). However, any noise reducing effect due to the recess 53 occurs at the region A in FIG. 7 and does not occur at any other part of the recess 53, because each rotor has a helical form and the recess 53 is a rectangle.